(1) Field of the Invention
The present invention relates to the field of rotorcraft, and more particularly to the field of ball joint assembly mechanisms between a connecting rod and at least one journal, in particular of a clevis.
(2) Description of Related Art
One specific application for such a ball-joint mechanism lies in it being incorporated in control apparatus of rotorcraft arranged to allow the pilot to transmit flight commands and/or operating commands to at least one rotor of the rotorcraft.
The present invention provides such a ball-joint mechanism that incorporates at least one lateral protection part that is interposed axially between the connecting rod and the journal. The protection part is more particularly of the type arranged as a one-piece ring or one-piece member of analogous shape for providing axial protection to the facing side faces of the connecting rod and of the journal.
In the field of rotorcraft, control apparatuses are commonly used to enable the pilot to transmit flight commands and/or operating commands for a rotor of the rotorcraft. Such control apparatuses comprise hinge mechanisms, and more particularly ball-joint mechanisms between at least one journal and a connecting rod. A ball-joint connection between the connecting rod and the journal allows them to move relative to each other both in pivoting and with lateral clearance.
The ball joint is made up of portions in relief having co-operating spherical bearing surfaces, comprising a ball arranged as a male member that co-operates with a cage of complementary shape. The cage and the ball are arranged respectively on the journal and on the connecting rod, or vice versa, the journal engaging at least axially against an assembly pin that carries one of the portions in relief having a spherical bearing surface. The journal may be a single journal or may form a component part of a two journal clevis with the connecting rod placed between the journals.
The assembly pin is commonly arranged as a bolt or an analogous axial assembly member that passes through a bore in the journal and that is blocked axially in position on the journal by axial clamping. In order to protect the bore of the journal through which the assembly pin extends, it is common practice to interpose a shouldered bushing radially between them. The axial blocking between the journal and the assembly pin may be obtained via the shouldered bushing. The shoulder included in the assembly pin is advantageously formed by the spherical bearing surface in relief that is carried thereby.
A general problem that arises lies in surface damage caused by the relative sideways movements between the connecting rod and the journal. The facing flanks of the connecting rod and of the journal are in danger of striking against one another when the connecting rod moves sideways with the consequence of damaging their corresponding side surfaces, or “flanks”, in use.
In order to solve that problem, it is common practice to interpose a lateral protection part axially between the connecting rod and the journal in order to preserve their facing flanks Such protection parts comprise wear masses made of soft material, a polymer material or some other analogous material. The wear mass serves to avoid damaging the more expensive materials from which the journal and the connecting rod are made. The protection part is designed to be replaced after it has been worn by more than an acceptable threshold.
Difficulties that need to be overcome lie in obtaining accurate and reliable assembly of the protection part when it is assembled on the ball-joint mechanism. Such assembly must also enable the protection part to be replaced quickly and easily when required.
The ball-joint mechanism must be structurally simple in order to avoid increasing the cost of making it, but without that harming its reliability or its length of life. The way the various members and parts making up the ball-joint mechanism are assembled together needs to be simple in order to reduce maintenance costs, in particular when replacing the protection part.
A traditional solution consists in securing the protection part constituted by said wear mass against the corresponding flanks of the journal and/or of the connecting rod by adhesive bonding. Such a solution presents the advantage of giving the protection part a structure that is simple and making it easier for the protection part to be assembled accurately and lastingly.
Nevertheless, arranging the ball-joint mechanism in that way makes replacement of the protection part once it has worn more complex, since such replacement involves a difficult operation of breaking the adhesive bond.
Another well-known solution consists in mounting the protection part so that it is floating on the assembly pin, being interposed axially between the corresponding flanks of the connecting rod and of the journal. Such a solution makes it easier to remove the protection part in order to replace it.
Nevertheless, that solution affects the accuracy with which the protection part is positioned on the mechanism because the part is free to move on the assembly pin. Such freedom of the protection part to move increases as it becomes more worn. The inaccuracy with which the protection part is assembled affects the reliability and the lifetime of the mechanism and can give rise to tensions on the parts making up the mechanism.
Proposals are made in document FR 2 951 511 (Eurocopter France) for a ball-joint mechanism between a clevis and a connecting rod that includes a lateral protection part incorporating a fastener member and a wear member. The fastener member and the wear member are secured to each other in a workshop by adhesive bonding. The fastener member is a deformable member used for fastening the wear member on the journal by elastic interfitting. Elastic deformation of the fastener member makes it possible to engage the protection part firmly against the journal. The wear member is secured to the fastener member in a workshop and the resulting protection part is then installed when assembling the ball-joint mechanism, the protection part being placed axially between the facing flanks of the journal and of the connecting rod.
Organizing the assembly of the protection part on the ball-joint mechanism in that way is advantageous in terms of the way it is fastened to the journal via the fastener member. The resulting fastening ensures accurate positioning and firm retention of the wear member in position on the mechanism, with this being independent of its degree of wear. Once worn, the protection part can be replaced easily and quickly by a technician, by elastically deforming the fastener member so as to withdraw one protection part and conversely install another one on the journal.
In practice, it has been found that such arrangements need to be improved in terms of simplifying the structure of the protection part and reducing the costs of obtaining it.
Nevertheless, any such improvement should obtain the looked-for advantages in terms of the difficulties and problems mentioned above. In particular, care must be taken to ensure that any improvements made still lead to accurate and reliable positioning of the protection part of the mechanism, both axially and radially. Care should also be taken that progressive wear of the protection part does not interfere with it being kept in position on the ball-joint mechanism.
Account should also be taken of the fact that maintenance on the ball-joint mechanism might lead to replacement of at least one of the spherical bearing surface members or indeed of the entire ball joint that connects together the two co-operating members having spherical bearing surfaces.
It is advantageous for a replacement of a ball-joint structure to be used to replace an existing ball-joint structure with a new ball joint that presents better performance and that is of a different structure. Such a difference in ball-joint structure relates in particular to its dimensions and/or to the materials from which one and/or more of the spherical bearing surface members are made. It is desirable for such a substitution to be easy to perform while limiting any effects on operations and on the advantages provided by the protection part.
Another difficulty needs to be taken into account with respect to managing stocks of the protection part itself and/or of the various parts that make it up. With the protection part being selected as a single piece comprising a fastener member and a wear member secured to each other, it is advantageous for the structure of the protection part to make it easier to manage the stocks of parts needed for producing it and that make it up.
The component parts of the protection part comprise in particular the fastener member and the wear member, and prior to them being secured to each other separate stocks of those parts need to be managed. The members constituting the protection part may be of various dimensions and possibly of various configurations depending on the protection part that is to be obtained for matching a particular ball-joint mechanism in which it is to be installed.
Such management of stocks of individual parts making up the protection part must be made easier, while also making it easy to adapt the protection part to almost any arbitrary ball-joint mechanism for a given general organization of the mechanism. The concept of any “arbitrary mechanism” should be considered with respect to the co-operating parts that make up the mechanism and that serve in particular to provide said ball joint.
The co-operating parts that make up the ball joint of the mechanism comprise in particular the journal, the connecting rod or at least any other spherical bearing surface in relief with which it is provided, and/or the assembly pin or at least the spherical bearing surface in relief associated therewith.
The management of stocks of the protection part itself must take account of the looked-for suitability of the protection part with respect to replacing the ball joint with a new ball joint of different structure.